Voice operated circuits



April 9, 1935.

B. G. BJORNSON 1,997,207

VOICE OPERATED CIRCUITS Filed April 22, 1932 2 Sheets-Shet 1 pawl/{:5}

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Patented Apr. 9, 1935 tU I Eo'sTATEs 1,997,207 VOICE OPERATED omcnrrs Bjorn G. Bjornson, Brooklyn, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New

York, N. Y., a corporation of New York Application April 22, 1932, Serial No. 606,814

\ e e fsclaims. (01. 178-44) Thisinventionrelates to transmission controlling arrangements and more particularly to arrangements for controlling the sensitivity of voice operated devices used in connection with trans- Tests have shown that steady currents such asthose set upin telephone circuits by induction from power linesor other adjacent circuits are a seriouslimitation on the sensitivity at which a voicei'operated circuit can be worked. :The seriousness of this difliculty becomes apparent when it is considered that'the sensitivity of such a circuit is limited by the noisiest circuit which i r may be connected to the line at a given time, while for other circuits which may be connected, a

greater sensitivity is possible; 'Also,"if the voice operated device is adjusted to maximum sensitivity withthe noisiest circuit, its sensitivity for as, v p

' ate with normal speech; If the indicator shows that the devices are" being maintained operated less noisy circuits will be reduced.

"It is an object of this invention to automatically'adjustjthe sensitivity of signal-controlled apparatus with changing noise conditions on the 1 line? with which such signal-controlled apparatus is associated; r

{I n is 'a-further object or this invention to maintain signal-controlledapparatus operable by signals only" even when noise currents are present in the signal lines in considerable volume;

In the manual operation of voice operated devices in telephone transmission systems, the op flerator is supplied with an indicator (such as a galvanometr). which" shows when the voice operated device operates. With experience, the ose ramruga sabout' how often and for what periods thevoice' operated devices should operlonger than normal speech should maintain them operated, it is known that noise is present in the line andis aiding in keeping the voice operated device's; operated. 'A loss is then introduced into the circuit thereby decreasing the sensitivity of the voice operated devices to noise currents but maintaining the devijcessensitive to voice currents/ fy The present invention consists of circuits and apparatuswhich simulate the operations of the manual operator and in addition, maintain the loss present in the circuit after the cessation of the noise currents fora timeto "avoid false operationswh'ichmight occur due to variations in the amplitude of the noise currents.

iswell' known the art, voice: currents havea 'syllabic'frequency which may vary from 2 to 22 cycles per secondgwhereas the noise cur PATENT OFFICE rents, against which the circuits to be described Y herein give protection, will usually consist of alternating or pulsating currents of a frequency higher than the cyllabic frequency and persisting continuously for approximately 1 second or longer. The circuit may be designed or adjusted however, to accommodate quitedifl'erent conditions.

The invention will be better understood from the following description and attached drawings forming a part thereof in which: Fig. 1. shows one form which the inventionmay take; and Fig. 2 shows another form utilizing but one relay; Each form is shown as applied to one side only of a four-wire transmission circuit, it being 1111-? derstood that suitable equipment will .be associated with the other'side of the line for a com plete installation.

Referring to Fig. 1, line L1 represents a oneway transmission line of a four-wire two-way system in which transmission occurs from left to right. i

Currents existing in line Lrare divided, aportion passing directly through delay. circuit l and amplifier 2, while the remaining portion. passes over conductors 3 and 4 and the primary winding of. input transformer 5. Resistances 6 and 'l are inserted in lines 3 and 4 to keep the currents shunted into them at the smallest value consistent with the proper operation of the associated circuits. 1

The secondary winding of transformer 5 .is connected to the input electrodes of a space discharge device 8'which is'adapted'to amplify the currents impressed thereon. 7

- The amplified output currents of device 8 pass in parallel through the primary windings of transformers 9, Ill and H. The secondary winding of transformer 9 is connected to the input electrodes of space discharge device l2 through resistances l3 and I4. Thev secondary winding of transformer i0 is connected to the input electrodes of space discharge device l51and the secondary winding of transformer H .is connected to the input electrodes of space "discharge device l6.

The output circuit of space discharge device I? includes the winding of relay l1 which is adapted to control a short circuit including armature I8 and contact 19 across line L1. Relay I1 is quick operating but has a release time suflicient to-cover the weak endings of the speech syllables. On normal continuous speech itwould regularly release between words. This release time canbe tlon of relay 25.

Relays {23-and 25 by means of their associated put circuit of space discharge device l5 includes the winding of relay 20 and the output circuit of device l6 includes the winding of relay 2|.

Relay 20 by means of its associated armature and contact controls current from battery 22 to operate relay 23. Relay 2| in a similar manner controls current from battery 24 for the operaarmatures and contacts control current from batteries 25 and2'l respectively for the operation of relays 28 and 29, respectively. Relays 28 and'29' by means of their associated armatures and con tacts control circuits which respectively insert biasing batteries 30 and 3| in the? input circuit of device l2 in parallel with resistances |3 and l4 to thereby vary the grid bias of device I 2 and hence its sensitivity.

Space discharge device I5 is so biased as to-be slightly more sensitive to impressed voltages than conversation relay "is maintained operated for approliimately one second, the currents causing this-willalso causethe operation of-the' train of relm'comprising relays 20, 23and 28 to increase the bias' of thegrid of device I 2. by, the voltage of-battery 30. If the amplitude of theincoming currents is sufllciently large and persist for the more! one-second, battery 3| is alsocut-in by mm 24, 25 and 29150 further increase the bias on the grid of device l2. The increased bias on em if willonly reduceitssensitivity tc'speech currents lyingbelow the noise margin. However, upon the 'dessation of speech, the anode current villi ceaseto now and relay will be de'energized, We ontube l2 being now solarge that the nbisec'urrents alone are insuflicient to maintain relay 'I'I' operated. The loss introduced- (grid compensates for the noise and device l2 and relay I! are desensitized as to noise while their sensitivity to voice currents is affected only inthe same energy range as the noise currents. rims-if the noise level is above a certain predetermined level for one second or morexthe ms'itivlty' of the voice-operated device is lowered ploring relays'2'0, 23.

- Speech will operate remys 2n and 2| but since their'relea'se time is short they will release durlag the pauses between words, The operating 3 timcof reiays 23 and25'is made long enough to guarantee that relays 20 and 2-| will release at least once during that time interval if speech is on the circuit in the absence of noise. The rate of speaking is normally about 3 or 4 words per second. The relays 20 and 2| will release at least once every second so that speech alone is unable to aifect the sensitivity of the voice operated devices.

Obviously other devices such as I5 and IS with decreased sensitivity and similar trains of relays may be added if desired to provide for varying the sensitivity in more than the two steps illustrated.

Referring now to Fig. 2, line Li corresponds to line L1 0! Fig. l and includes delay circuit 3| and amplifier 32. An amplifier 33 connected to line L1 ina manner similar to amplifier 8 of Fig. 1 has included in parallel in its output circuit the primary windings of transformers 34 and 35. The seccndarywinding of transformer 34 is connected through biasing battery 36 to the input electrodes of detector 31 corresponding to device |2 of. Fig. I. The output circuit of detectbr'fl includesthe usual anode battery 38 and the-ope crate windin'gof relay 39. Relay 39 is adjusted toperform the same function as relay I'I ofFig. 1,- that is, the operation of relay 39by means-oi its armature and associated contact removes a short circuit normally existing across line L1 in the output of amplifier 32.

The secondary winding of transformer is connected tothe input electrodes of space discharge device 48. These connections include space-discharge rectifier 49, condenser 50 androsistance'5l. The anode of device is-connected to thegrid of device 40 through'anode battery 4| and gridbias battery 42. The cathodes of all these devices are connected in series as shown. A condenser 43- and resistance 44 are connected across the input electrodes of device 40.

The output circuit of device 40-includesanode batters/'45, resistance'46 and bias" winding of relay 3,9; A condenser 41' is connected in parallel to resistance and biaswinding of relay- 39-. The bias winding'of relay 33 1s wound as to oppose the effect of the operate winding. 3

In one embodiment of the invention, devices 49, 48 and-lo'and" associated circuits were arranged so that device 49 operated inabout;.001 sec. and continuedupon cessation of input energy about .05 sec. Device 48 required about 1.0-sec. to operate and about .01 secQtorelease, anddcvice operated in about .01 sec.and released-in aboutlO sec. Using the phraseology applied to the relays of Fignl, device 49 is quick operate, slow release; device 48 slow operate, quick release; and device 40 quick operate, slow release. The circuits by means of whichthese operate and release times are obtained are described in more detail hereinafter. Y

Some of the amplified output of amplifier 33-18 impressed uponv device 31 in the well known man nor by the secondary winding of transformer 34. The output circuit of device 31 includes the operate winding of relay-39' and passage of current in this output circuit energizes relay 38 andthe short circuit across line L1 is opened, permitting speech to pass on. As is well known, the delay circuit 3| retards the passage of currents therethrough long enough to permit the operation of relay 39. I

The remainder of the output of amplifier 33 is impressed on device, the input circuit of which includes rectifier device" and resistance 5| and condenser 50. Current passing through rectifier 49 and resistance 5| causesa negative bias to be impressed uponthe grid of device 48'. As stated above, the characteristics of condenser 50 and resistance are such that device 49 acts quickly to change the bias on the grid of device 48.

The increased negative bias on the grid of device 49 causes a decrease in its anode current. However, as the anode current decreases with continued incoming line current through ampliher 33, condenser 43- discharges, maintaining a flow of current through resistance 44 for an appreciable time (one second) and thegrid bias of device 40 remains substantially unchanged. If the line current persists for as long as one second the grid bias of device 40 is changed causing anode current to flow therethrough and the energization of bias winding of relay 39.

lThe constants of the circuit including devices 49, 48 and 40 are such that-the magnitude of the current passing through the bias winding "of relay 99 is proportional to. the magnitude of the noise currents.

, The similarity of operation of the circuit of Fig. 2 to that of Fig. 1 is obvious.

The time constants which were characteristic of the relays in Fig. l are supplied by the space discharge devices andassociated circuits.

The desensitizing action occurs in relay 39 due to its opposed windings, that is, if noise currents are present so that relay 39 would be maintained operated upon the cessation of speech, these currents are opposed in the bias winding so that relay 39 is desensitized as to noise.

As in Fig. 1, a circuit is provided for main taining the desensitizing means operated for a considerable time (e. g., ten seconds) after the cessation of the actuating currents. In Fig. 2, this function is accomplished by thecircuit comprising condenser 41, resistance 45, and the bias winding of relay 39. The characteristics of these elements are such that the current flow through the relay winding and resistance 46 when condenser 41 .is discharging (upon cessation of current flow in the anode circuit of device 40) will maintain a bias on the relay for approximately ten seconds. Since relay 39 is maintained biased forthis extended period, false operation due to varying noise currents is greately minimized.

,Ha'ving described the invention and the advantages thereof in one particular embodiment,

' it is to be understood that the invention is to be limited only by the scope of the appended claims.

What is claimed is: 1. A transmission system comprising line wires upon which both noise and voice currents may be impressed, a circuit comprising parallel branches connected to said line wires, space discharge devices in said branches, the amplitude of the output of said branches being proportional to the amplitude of the actuating currents, and a two-winding relay having contacts which control the continuity of said line wires, said windings being arranged in opposed relation, one of said windings being included in the output circuit of said first branched circuit, said second winding being included in the output of said second branched circuit whereby the output currents of said second branched circuit cause said relay to be less sensitive to the output currents of said first branched circuit, a resistance in series with said second relay winding and a condenser in shunt to said resistance and said winding, said condenser and said resistance having such values that said winding is maintained energized for ten seconds after the cessation of the currents causing the operation of said second branched circuit.

2. A transmission system comprising a line for the transmission of speech waves, means controlling transmission along said line, means responsive to speech waves on the line for operating said controlling means, means opposing actuation of said controlling means, means relatively unresponsive to speech waves but responsive to energy on the line of more sustained characteristic than speech waves, for causing actuation of said opposing means, said last mentioned means when operated maintaining said opposing means operated for a period of the order of ten 

